1. Field of Invention
The invention relates to a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device having an improved aperture ratio and a method of fabricating the same.
2. Discussion of Related Art
Recently, liquid crystal display devices have been spotlighted as next generation advanced technology display devices because of their low consumption in power, high portability, and high added value.
Generally, a liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field across the liquid crystal molecules.
In other words, as the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling the light transmittance of the liquid crystal material.
The LCD device includes thin film transistors as a switching element, referred to as an active matrix LCD (AM-LCD) device. Therefore, the LCD device has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely used.
The AM-LCD device includes an array substrate, a color filter substrate and a liquid crystal layer interposed therebetween. The array substrate may include a pixel electrode and thin film transistor, and the color filter substrate may include a color filter layer and a common electrode. The AM-LCD device is driven by an electric field between the pixel electrode and the common electrode to have excellent properties of transmittance and aperture ratio. However, since the AM-LCD device uses a vertical electric field that is perpendicular to the substrates, the AM-LCD device has poor viewing angles.
An LCD device having a wide viewing angle property has been suggested and developed to resolve the above-mentioned limitations.
FIG. 1 is a cross-sectional view of a related art in-plane switching (IPS) mode LCD device. As shown in FIG. 1, the related art IPS mode LCD device includes an upper substrate 9 and a lower substrate 10 spaced apart from and facing each other. A liquid crystal layer 11 is interposed between the upper and lower substrates 9 and 10. A common electrode 17 and a pixel electrode 30 are formed on the lower substrate 10. The common electrode 17 and the pixel electrode 30 may be disposed on the same level. Liquid crystal molecules of the liquid crystal layer 11 are driven by a horizontal electric field L, which is induced between the common and pixel electrodes 17 and 30.
FIGS. 2A and 2B are cross-sectional views showing turned on state and turned off state, respectively, of a related art IPS mode LCD device. FIG. 2A shows arrangement of liquid crystal molecules in on state, when the voltage is applied to the IPS mode LCD device, arrangement of liquid crystal molecules 11a above the common electrode 17 and the pixel electrode 30 is unchanged. However, liquid crystal molecules 11b between the common electrode 17 and the pixel electrode 30 are horizontally arranged due to the horizontal electric field L. Since the liquid crystal molecules 11b are arranged by the horizontal electric field L, the IPS mode LCD device has a wide viewing angle property. For example, the IPS mode LCD device has a viewing angle of about 80 degrees to about 89 degrees up and down and right and left without an image inversion or a color inversion.
FIG. 2B shows the state where the voltage is not applied to the IPS mode LCD device. Because an electric field is not induced between the common and pixel electrodes 17 and 30, the arrangement of liquid crystal molecules 11 of the liquid crystal layer is not changed.
FIG. 3 is a cross-sectional view schematically illustrating a pixel region of a related art IPS mode LCD device. As shown in FIG. 3, the related art IPS mode LCD device 95 includes an array substrate 40, a color filter substrate 70, and a liquid crystal layer 90 interposed between the substrates 40 and 70.
The array substrate 40 includes gate lines (not shown) formed along a horizontal direction, common lines (not shown) parallel to the gate lines, and data lines 50 intersecting the gate and common lines (not shown). A gate insulating layer 48 is disposed between the data line 50 and the gate and common lines. The gate lines and the data lines 50 define pixel regions P.
A thin film transistor (not shown) is formed in each pixel region P and includes a gate electrode (not shown), a semiconductor layer (not shown), and source and drain electrodes (not shown). A passivation layer 60 covers the thin film transistor (not shown).
A plurality of pixel electrodes 64 and a plurality of common electrodes 62 are formed in the pixel region P on the passivation layer 60. The pixel electrodes 64 are electrically connected to the drain electrode (not shown) of the thin film transistor (not shown) through a drain contact hole (not shown), which exposes the drain electrode (not shown). The common electrodes 62 are connected to the common line (not shown) through a common contact hole (not shown). The pixel electrodes 64 and the common electrodes 62 each have a bar shape and alternate each other.
Here, the pixel electrodes 64 and the common electrodes 62 on the passivation layer 48 have a single layered structure of a transparent conductive material or an opaque metallic material.
The color filter substrate 70 corresponding to the array substrate 40 includes a black matrix 73 having an opening corresponding to the pixel region P and a color filter layer 76 in the opening of the black matrix 73. The color filter layer 76 includes red (R), green (G) and blue (B) color filter patterns 76a, 76b, and 76c that are sequentially repeated.
An overcoat layer 78 covers the color filter layer 76. A gap-forming spacer (not shown) having a first height and a press-preventing spacer (not shown) having a second height are formed at a border of the pixel region P. The second height is lower than the first height.
In the IPS mode LCD device 95, when the array substrate 40 and the color filter substrate 70 are attached, there may be misalignment. Therefore, to prevent light leakage, the black matrix should have a wider width due to an alignment margin between the array substrate 40 and the color filter substrate 70. Accordingly, the aperture ratio is lowered.